The SWAS instrument consists of the moving telescope assembly, the interface baseplate assembly, and the thermal control housing. The movin g telescope structure holds the primary mirror, secondary mirror, and receiver front end in precise alignment. This structure also carries the receiver cold plate radiators, which view cold space both directl y and through reflection off the primary mirror. The moving telescope assembly attaches to the interface baseplate with an open pivot frame through which flex leads from the receiver front end also pass. Two flexure-mounted linear actuators tilt the moving telescope assembly u p to +/-3 deg in two axes. The interface plate serves as a mounting for these actuators as well as the acousto-optic spectrometer, the inst rument control electronics, the star tracker, and the balance of the receiver components. The thermal control housing attaches to the inte rface baseplate around its edge. The top cylindrical part of this hou sing serves to shade the receiver cold plate radiators from Sun and Earth influence. The bottom "D" shaped portion of the housing is therma lly isolated from the top and forms the electronlcs radiator. Heat is conducted from the Interface baseplate into this lower portion of the shell. The radiator geometry and conduction paths create a very stab le thermal environment in the center of the interface baseplate where the AOS and receiver IF amplifiers are heat sinked. The outer surface of the thermal control housing is covered with fused silica second s urface mirrors that reflect visible light and radiate infrared energy . The instrument is mounted to the spacecraft through four thermally- isolating titanium flexures an the underside of the interface basepla te.